Method and system for reducing longitudinal fluid flow around a permeable well

ABSTRACT

A method for reducing longitudinal flow of fluids through an annular space surrounding a permeable well tubular, such as a slotted liner or a sandscreen, in an inflow region of an oil and/or gas production well having: arranging a series of collapsed resilient sealing rings at regular longitudinal intervals around the permeable tubular before lowering the tubular into the well by means of tape and/or a binder which dissolves downhole; placing the tubular in the inflow region of the well; and allowing the tape and/or binder to dissolve, thereby allowing the resilient sealing rings to expand radially in the annular space surrounding the permeable tubular.

FIELD OF THE INVENTION

The invention relates to a method and system for reducing longitudinalflow of fluids through an annular space surrounding a permeable welltubular, such as a slotted liner or a sandscreen, in an inflow region ofan oil and/or gas production well.

BACKGROUND OF THE INVENTION

Modern wells have inflow regions which may have a length up to tenkilometers. In these inflow regions elongate permeable tubulars such asslotted liners, expandable slotted tubulars and/or sandscreens may bearranged which preserve the integrity of the borehole and prevent influxof solids and erosion of the borehole wall during production of oiland/or gas.

However, around these permeable tubulars an annular space of aconsiderable length may be present or created during production as aresult of erosion. This erosion may increase as the eroded annulus mayincrease in length and width and as a result in some wells the fluidflow through the annulus is equal to or even larger than the productionthrough the interior of the permeable tubular.

Logging procedures which employ downhole spinners that are rotated bythe fluid flux inside the tubular will not detect the addition fluidflux through the annulus and may therefore create an Impression that theinflux in some regions of the well is smaller than it is in reality.Ultimately this has led to limited production campaigns.

U.S. Pat. No. 4,576,042 discloses a flow basket comprising an umbrellatype configuration of petals which are expanded by moving a sleeverelative to a shaft. U.S. Pat. No. 5,033,551 discloses a frusto conicalcup which is released downhole by removing a sleeve from the cup afterplacement of the cup at the top of a wellscreen in a well.

A disadvantage of the known methods is that they require downholemanipulation of well equipment which is a complex and time consumingprocedure that is not suitable for installation of a series of seals atshort intervals along the length of an inflow region of a well.

SUMMARY OF THE INVENTION

The present invention aims to solve the problem of longitudinal annularflow around permeable well tubulars in an economical and effectivemanner.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail, by way of example withreference to the accompanying drawings in which the examples should notbe construed to limit the scope of the invention.

FIG. 1 is a schematic three-dimensional view of a horizontal inflowregion of a well in which a production liner is present which isequipped with a series of sealing rings according to the invention;

FIG. 2 is a side view, at an enlarged scale, of one of the sealing ringsand a section of the production liner shown in FIG. 1;

FIG. 3 is a side view of an expanded alternative embodiment of a sealingring according to the invention which is wrapped around a productionliner during installation; and

FIG. 4 is a side view of the sealing ring of FIG. 3 in its expandedform.

DETAILED DESCRIPTION OF THE INVENTION

The method according to the invention comprises:

arranging at least one resilient sealing ring around the permeabletubular before lowering the tubular into the well;

constraining the ring in a collapsed position around the tubular bymeans of a tape and/or binder which gradually dissolves in a downholeenvironment;

placing the tubular in the inflow region of the well; and

allowing the tape and/or binder to dissolve thereby allowing at leastpart of the resilient sealing ring to expand radially in the annularspace surrounding the permeable tubular.

Preferably a series of resilient sealing rings are arranged at regularlongitudinal intervals along the length of the permeable tubular andeach sealing ring has one end which is permanently clamped to thepermeable tubular and a resilient lip-shaped other end which istemporarily clamped around the tubular during installation of thetubular in the well and which is released after installation such thatthe resilient lip-shaped other end unfolds itself and expands radially.

In such case it is preferred that the resilient lip-shaped other end ofeach sealing ring is temporary clamped around the tubular duringinstallation using a tape and/or binder which dissolves gradually in thedownhole environment.

During installation the lip-shaped ends of the sealing rings may faceforward, i.e. against the running direction, and are collapsed tightlyagainst the outside of the tubular by using a suitable metal binder,restrainer and/or tape. The metal binder or restrainer or tape may havea melt point just below the static temperature of the closed-in well.Alternatively the tape may be made of a polymer that slowly dissolves inthe downhole environment, such as natural rubber which dissolves inaromatic oils. If required wash cocktails can be designed to enforce theremoval of the restraining binder or tape. Thus, after installation andflushing away of the restraining binder or tape the resilient lip-shapedend of the sealing ring will unfold in the annular space between thepermeable well tubular and the open hole, thus diverting fluid flow intothe tubular. The folded sealing rings may be run in combination with astand-off and/or inside a bow spring centralizer to avoid damage whilerunning in.

The system according to the invention comprises a series of sealingrings arranged at regular longitudinal intervals around a permeable welltubular, each ring having one end which is permeably connected to theouter wall of the tubular and another resilient lip-shaped other end.

The invention will be described i more detail, by way of example withreference to the accompanying drawings in which:

DETAILED DESCRIPTION OF THE DRAWINGS

Referring now to FIG. 1 there is shown a gas and/or oil production well1 which traverses an underground formation 2. The upper, substantiallyvertical, part of the well comprises a casing 3 which is cemented inplace, The lower, substantially horizontal, inflow zone of the well isprovided with a slotted production liner 4 which is secured to the lowerend of the casing 3 by an expandable annular packer 5.

The production liner 4 is provided with a series of expandable sealingrings 6 which are distributed at regular intervals along the length ofthe production liner 4. As shown in FIG. 2 each sealing ring 6 consistsof a swab-cup of which the free end 7 faces the borehole wall 8 and theother end is secured to the liner 4 by a hose clamp 9.

The sealing rings 6 urge the oil and/or gas that flows into the wellboreto flow in a substantially radial direction through the annulus 10 andthe slots 11 into the interior of the liner 4, so that longitudinal flowof fluids through the annulus 10 is minimised.

In the region of each sealing ring 6 the liner 4 is unslotted to providerigidity and to provide an area where accurate flow measurements can bemade within the liner 4 by e.g. a spinner or injection of tracerchemicals.

To protect the sealing rings 6 during the descent of the liner 4 throughthe wellbore 9 the free ends 7 of sealing rings 6 are wrapped around theliner 4 by a tape (not shown) before installation. The tape may be madeof a plastic which slowly dissolves downhole and/or may be provided witha bonding agent that looses its bonding ability downhole so that thetape is released and removed and the free end 7 expands against theborehole wall 8 when the liner 4 has reached its downhole destination.FIGS. 3 and 4 show an alternative embodiment of a sealing ringconfiguration according to the invention. In this embodiment the sealingring comprises a rubber or other elastomeric membrane 20 which isexpanded like an umbrella by means of a series of spring blades 21 whichare secured at their downstream end to the outer wall of the productionliner 22.

The arrows illustrate in FIG. 3 how the expanded membrane 20 provides afluid seal in the annulus 23 surrounding the production liner 22 thatminimizes longitudinal flow through the annulus 23 and promotes thefluids to flow directly through the slots 24 into the liner 22.

FIG. 4 shows how the membrane 20 and spring blades 21 are, duringdescent of the liner into the well, wrapped around the liner 22, bymeans of a tape 25 which slowly dissolves downhole. Protection rings 26and 27 protect the unexpanded sealing ring from damage as a result ofthe movement of the liner 22 through the borehole during installation.

It will be understood that the spring blades 21 may overlap each othersuch that a diaphragm type of expandable sealing ring is created, inwhich case the membrane 20 may be omitted.

1. A method for reducing longitudinal flow of fluids through an annularspace surrounding a permeable well tubular-in an inflow region of an oiland/or gas production well, the method comprising: arranging at leastone resilient sealing ring around the permeable tubular before loweringthe tubular into the well; constraining the ring in a collapsed positionaround the tubular by means of a tape and/or binder which graduallydissolves in a downhole environment; placing the tubular in the inflowregion of the well; and allowing the tape and/or binder to dissolvethereby allowing at least part of the resilient sealing ring to expandradially in the annular space surrounding the permeable tubular.
 2. Themethod of claim 1, wherein a series of resilient sealing rings arearranged at regular longitudinal intervals along the length of thepermeable tubular.
 3. The method of claim 2, wherein each sealing ringhas one end which is permanently clamped to the permeable tubular and aresilient lip-shaped other end which is temporarily clamped around thetubular during installation of the tubular in the well and which isreleased after installation such that the resilient lip-shaped other endunfolds itself and expands radially.
 4. The method of claim 3, whereinthe resilient lip-shaped other end of each sealing ring is temporaryclamped around the tubular during installation using a tape and/orbinder which dissolves gradually in the downhole environment.
 5. Themethod of claim 3, wherein permanently clamped end of each sealing ringis located downstream of the resilient lip-shaped other end of the ring.6. A sealing system for use in the method for reducing longitudinal flowof fluids through an annular space surrounding a permeable well tubularof claim 1, said system comprising a series of sealing rings arranged atregular longitudinal intervals around a permeable well tubular, eachring having one end which is permeably connected to the outer wall ofthe tubular and another resilient lip-shaped other end.